This invention relates to electronic apparatus mounted as in a vehicle, and particularly to an improved method of attenuating shock and vibration between the vehicle and the printed circuit board components in the apparatus.
In a vehicular installation, several considerations must be taken into account. There must be a strong, rigid structure for supporting the weight of the apparatus within a vehicle which is subject to constant vibration-- severe vibration in the case of off-the-road vehicles. Since electronic devices, no matter how well designed and constructed, are still subject to damage from vibration, it is desirable to attenuate this vibration as much as possible before it is transmitted to the most vulnerable parts of the apparatus.
In the prior art, most such equipment has the chassis structure attached directly to the support structure, so that a direct path for vibration exists from the vehicle to the chassis and its attached components. Thus, if the mounting threads which are tapped into the chassis wall become damaged or stripped, as by cross-threading, the entire chassis unit has to be replaced at considerable trouble and expense.
In an effort to solve some of these problems, metal mounting inserts have been molded into the walls of the housing, producing attenuation in the amount of vibration reaching the chassis components, since a resilient housing will absorb a considerable amount of vibration. The cross-threading problem was reduced but not solved, since damaged mounting threads still required replacing at least a portion of the housing. Also, the cost of the housing is increased for two reasons. First, a separate, hand operation is required in that, before molding, a metal insert must be carefully positioned by hand within each mold before the plastic is injected. More important, injection molding one substance around another, e.g. plastic and metal, tends to cause problems such as deformation or short filling. For the latter reason, the incidence of rejects is greatly increased. Also, the walls of the housing must be heavier in the area of a molded insert, making the walls less resilient and reducing the vibration attenuation.